On the mechanism of high-temperature oxidation of ODS superalloys: Significance of yttrium depletion within the oxide scales

The oxidation behavior in air of two ODS superalloys, the chromia-forming P M 1000 and the alumina-forming PM 2000, was investigated at temperatures be tween 900 and 1300 degrees C. For both allays growth rates of the oxide sca les obey a subparabolic time dependence and an Arrhenius-type temperature d ependence of the rate constants is observed. Diffusion of yttrium to the su rface of the oxide scales leads to almost complete depletion of this elemen t within the oxide scales of both alloys. Scale growth then takes place by simultaneous inward diffusion of oxygen and outward diffusion of cations. A t this stage of the oxidation process, the scale-growth mechanism is simila r for both ODS alloys, at least in a qualitative way, to conventional (non- ODS) alloys of the same base composition.